Filtering is an important aspect of many transceivers. In some systems a signal is received that has two components: a desired signal in a frequency band of interest and an undesired signal that occupies all other frequencies and may be much larger than the desired signal (sometimes referred to as “blockers”). When the desired signal is bandpass in nature (i.e., the frequency band it occupies has a center frequency larger than zero and has a bandwidth less than twice the center frequency) it is sometimes necessary to create a sharp filter that attenuates the blockers while maintaining the integrity of the desired signal. Furthermore, often times programmability is also desirable since the transceiver may be required to operate on various input signals in various frequency bands. Building a filter with a sharp cut-off that is widely programmable is very difficult. One technique that is often used is to build a filter at a specific (i.e., fixed) frequency or a filter that covers a relatively small range of frequencies and use a mixer to translate the desired signal from its frequency band to the center frequency of the filter.
One major issue that occurs in this process of mixing is that the clock used in mixing is composed of a fundamental frequency as well as its harmonics. These harmonics can cause lots of problems including translating undesirable information directly on top of desirable information. It would be desirable to develop techniques that minimize this issue.